1. Field of the Invention
The present invention relates to a bolometer, and more specifically to a compensation circuit for compensating non-uniformity due to the difference of operating temperatures between bolometers existing in a bolometer array using semiconductor material.
2. Description of the Background Art
FIG. 1 generally represents an IR (Infrared) detector configured by a bolometer with an array of 3×3(3 rows 3 columns) using a semiconductor process.
As shown in FIG. 1, the IR (Infrared) detector configured by the bolometer with the array of 3×3 (3 rows 3 columns) is formed using the semiconductor process. However, it detects respectively different values, which are the temperatures of each bolometer arranged in each array that varies from 301.9° K to 302.3° K, when the temperature of a material is 300.00° K.
Although the bolometer is configured using a semiconductor process, it is not an accurate IR detector because the characteristics per pixel configuring each bolometer are different from each other because of factors, such as material characteristics or change of process.
To solve the described problem, the 2-point amendment method shown in FIG. 2 is used.
FIG. 2a to FIG. 2c represents an amendment process to explain the related art of the 2-point amendment method.
As shown in FIG. 2a, the graph represents that the off-set amendment and the gain-amendment have not been performed in the 2 point method amendment circuit.
Line A represents a value in which an actual bolometer operates, while line B represents a reference value in which a bolometer should operate regardless of operating temperature changes.
The magnitude (offset) and gradient (gain) of line A needs to be changed to have the same magnitude and gradient of line B.
The graph in FIG. 2b illustrates that the 2 point amendment method initially amends the first off-set between Line A and Line B.
Offset amendment means that the magnitude of line A is altered by amending the magnitude (offset) of line A to intersect at the point Qmin within the dotted circle of FIG. 2b. 
The graph in FIG. 2c illustrates that the 2 point amendment method then amends the second gain between Line A and Line B.
The second amendment is performed by altering the gradient (gain) with the reference point Qmin for the off-set amended by the process of FIG. 2b. 
As described above, the coefficient of the bolometer may be compensated to ideally operate regardless of temperature in the bolometer, by amending the first off-set and amending the second gain.
The 2-point method amendment, however, has a critical problem in that the non-uniformity of reactivity on the operating temperature existing on the bolometer material itself cannot be substantially amended.
An additional problem is that when the 2-point method amendment is performed, the operating temperature of the IR detector must be constantly maintained as the 2-point method is only efficient when the IR detector operating temperature is constantly maintained.
A thermoelectric cooler may be used to ensure that the operating temperature of the IR detector remains constant. However, using a thermoelectric cooler increases power consumption, volume, and costs.
If a thermoelectric cooler is not used, to maintain the operating temperature of the IR detector, the 2-point method amendment will not be able to eliminate above described non-uniformity problem.
To solve the non-uniformity problem, a bias equalization method shown in FIG. 3 is suggested.
FIG. 3 represents the bias equalization method for amending the non-uniformity generated by the change in the operating temperature of pixel composed of conventional bolometer.
As shown in FIG. 3, the bias equalization method is a method where a bias voltage capable of reducing non-uniformity is applied to each bolometer IR detector through Digital-to-Analog Converter 1 (DAC1) DAC1 as a voltage. This method performs an off-set amendment using DAC2 in the first step, and then, performs a gain amendment using DAC2 in the second step.
The gain amendment coefficient is multiplied, and the off-set level existing among the pixels is deleted to amend the gain of each pixel. As a result, non-uniformity of bolometer on IR input may be compensated.
Although the range of amendable temperatures is broader than that of conventional 2-point method, non-uniformity of reactivity on operating temperature existing bolometer material itself cannot be substantially amended. Hence, the need for maintaining temperature of system using bolometer cannot be substantially eliminated.